Apple maggots

How to identify apple maggot

• The adult fly is 1/4 inch long, smaller than a common housefly.
• It has dark markings on the clear wings and a conspicuous white spot where the thorax joins the abdomen.
• It has three (male) or four (female) white stripes on the abdomen.

Life cycle of apple maggot

Adult apple maggots begin to emerge from the soil around late June to early July, and continue through most of the summer.

• Adult flies often leave an orchard area to feed in wooded or brushy areas.
• Adult females return to lay eggs just under the skin of apples.
• Each female fly can lay hundreds of eggs.
• Once eggs hatch, larvae feed for three to four weeks.
• When apples drop to the ground, the larvae transform into pupae in the soil.
• Pupae spend the winter underground, emerging as adults the following summer.

Damage caused by apple maggot

• Apple maggot flies lay eggs in fruit, which becomes pitted and misshapen.
• The female fly creates a "sting” or hole as she lays an egg; each one forms a tiny spot or dimple.
• Maggots (larvae) tunneling through the flesh break down the pulp, which discolors and starts to rot.
• Larvae are rarely seen, but are much smaller than other apple pests like coddling moth larvae.

How to protect your trees from apple maggots

Keep your garden or orchard clean

• Remove any apples that fall during the growing season and after harvest.
• Put fallen apples in a sealed container and remove them from your site by putting them in the trash or sending them to a municipal composting site.
• Do not compost them in your yard or orchard.

• Note: Removing overripe and rotten apples from around your trees can help reduce apple maggot infestations, but it will not prevent apple maggot flies that come in from other areas.

Bag apples

This method was developed in western Minnesota and is suitable for gardeners who have one or a few medium-sized trees. If you have a tall tree, you may choose to bag only the fruits that are easy to reach, and let the apple maggots have the fruit growing higher up.

Bagging fruit takes extra time; however, the apples are protected from apple maggots for the rest of the season.  

• Apply the bagging method after you have thinned your fruit to one apple per cluster. It can be done sometime between early and mid-June.
• Enclose each apple in a plastic sandwich bag, either a zipper closure bag or a plain bag closed with staples. You can also buy fruit protector bags. 
• If you are using sandwich bags, snip the bottom corners off each bag with a pair of scissors to leave a very small opening for water to run out.
• At harvest, remove the bag and dispose of it.

Sticky traps

Apple maggot traps are red spheres coated with tanglefoot, a sticky substance that permanently holds insects. They are typically used to monitor populations in commercial orchards, but strategically hanging traps on the outer canopy of apple trees can help capture apple maggot females that attempt to lay eggs on the fruit.

Types of apple traps and lures

• Wooden or plastic spheres painted red.
• Red plastic spheres sold specifically for this purpose.
• Store-bought large, red, fresh apples coated with tanglefoot. Compost them at the end of the season. Apples naturally act as a lure due to the aromas they produce.
• The Ladd trap is a red sphere and yellow rectangle combination. This trap may be more effective in catching apple maggot flies, even though they can be harder to clean. 
• Commercial lures can be purchased and placed inside a red plastic sphere. Alternatively, an apple chunk can be placed inside the sphere.  

Whichever type of trap you choose, the spheres or apples should be at least 3 inches in diameter and bright red.

• Hang up traps outside of your apple trees, or on the edges of the tree canopy. Hanging a single trap inside of a tree may attract flies without catching every fly. 
• Wooden and plastic spheres can be hung with an eye screw and wire hook, while fresh apples can be hung by skewering the apple with a coat hanger and bending the excess wire into a hook.
• If hanging traps on the outside of a tree canopy, aim to hang one trap per 100 fruit (after thinning) for each tree.
  • One or two spheres for small trees and five or more traps for larger trees.
  • Place at least one trap on the side of the tree that faces any wooded or brushy area.
  • A second trap should hang on the south side of the tree.

To further reduce apple maggot pressure, hang traps in apple or hawthorn trees in nearby wooded or landscaped areas.

• Hang traps in the trees by the end of June to catch the apple maggot flies as they first attempt to lay eggs.
• Remove any leaves or fruit touching the traps.
• Check all the traps weekly. Clean off the tanglefoot-coated insects and apply more tanglefoot as needed.

Note on removing tanglefoot coating: This can be one of the least appealing parts of using traps. Instead of replacing tanglefoot on actual apples used as traps, simply throw them away or compost them. If you want to reuse a trap:

• Start by wearing disposable gloves to prevent getting your hands sticky.
• Using an old rag and any vegetable oil, rub the tanglefoot off the trap.
• Wash the trap in warm water with dish soap.
• Adhesive removers like orange oil can also help remove tanglefoot.

Kaolin clay

Kaolin clay can discourage apple maggot flies and other insects from laying eggs in apple trees. This method is best used with traps and before any pesticide application. 

• Before applying kaolin clay products, read the label and use equipment that is less likely to get clogged up. Maintain equipment to prevent erosion.
• Apply clay in a visible layer to all surfaces of the tree, leaves and fruit. This acts as a visual and physical repellent to insects.
• Apple maggot females are attracted to the red color of ripening apples, so a grayish-white apple is not attractive.
• The layer of clay on fruits repels many insects.
• Clay washes off easily even in moderate rain and will likely need to be reapplied. 
• A well-maintained coating of kaolin clay can protect 90 percent of fruit from apple maggots but requires more effort than other methods.’

Tree exclusion netting

The University of Minnesota has recently researched hail netting, or exclusion netting, as a method to keep pests like apple maggot and codling moth out of apple tree canopies. For this to work, the whole tree must be wrapped in netting, or housed in a netting tent.

• Netting should be applied after bloom so it does not interfere with pollination, and after fruits have been thinned.
• Netting works best for smaller trees.
• Trees must be fully enclosed to exclude apple maggots.
• UMN research found an average 96% exclusion of apple maggots using hail netting in a commercial orchard setting. 
• Netting is sold commercially by many vendors.
• Remove the netting right before harvest and store it in a dry place for the next season.

Pesticides

Check for apple maggots using sticky red spheres. This will help you decide if you should apply a pesticide. For commercial orchards, programs like Cornell’s Network for Environmental Weather Applications can help you keep track of insect populations and their current life stages. Avoid calendar spraying to lower the incidence of killing beneficial insects.

When checking your traps:

• Check the trap frequently.
• If you do not use a scent lure, spray for apple maggots as soon as you catch a single adult.
• If you hang a trap with a lure, wait until you have caught a total of five flies.

Effective pesticides for apple maggot control include products that contain esfenvalerate, carbaryl, and spinosad. Carbaryl is a general broad-spectrum insecticide that should be used strategically to prevent unnecessary killing of beneficial insects.

For commercial growers, refer to the most updated version of the Midwest Fruit Pest Management Guide for more guidance about pesticide effectiveness and availability for apple maggot management. Entrust is one pesticide option available for organic management, and is most effective when used while populations are low.

Home gardeners may want to remove traps before applying any insecticide.

• After a single insecticide application, traps should be renewed by replacing tanglefoot.  
• Spray again as you continue to check traps for new catches and repeat the whole process as needed.
• You might have to spray for apple maggot three or four times per season.

Fortunately, the number of apple maggot adults decreases as the season progresses, and you should be able to stop spraying after flies stop being caught in traps.